Void defects under track slabs are the main danger affecting the safe operation of high-speed railways. In the short high-speed railway maintenance periods, China’s high-speed railway line maintenance operations must quickly and dynamically determine void defects under track slabs that are in service without contact. However, the detection of void defects under track slabs still mainly relies on the manual inspection and flaw detection by railway workers during the railway maintenance period. If the defects are not quickly identified, the consequences could be disastrous. This article presents a new method for the non-contact dynamic detection of void defects under track slabs. The method involves the use of air-coupled ultrasonic sensors to generate and receive ultrasonic guided waves in the track slab to quantitatively represent the size of the void defect according to the principle of energy leakage of guided waves in the propagation process. The characteristics of the position-amplitude curve, taking the position of the beam axis as the abscissa and the amplitude of the time domain signal as the ordinate, were numerically calculated and analyzed. The quantitative relationship between the convex interval of the position-amplitude curve and the size of the void defect was obtained, and an imaging method of the void defects based on x, y two-dimensional line scanning data fusion is proposed. The excitation and reception methods of air-coupled ultrasonic guided waves were studied, and a 1:1 model of the track structure was built in the laboratory to verify the method and detect the void defect under the track slab. The experimental results show that ultrasonic guided waves can be excited and received in the track slab by air-coupled ultrasonic sensors. Based on the guided wave energy leakage principle, the quantitative characterization and imaging of the void defect under track slabs can be realized.

中文翻译：

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空气耦合超声波传感器检测轨道板下空洞缺陷的新方法

轨道板下空洞缺陷是影响高速铁路安全运营的主要危害。在高速铁路维修周期较短的情况下，我国高速铁路线路维修作业必须快速、动态地确定在役轨道板下的空洞缺陷，而无需接触。然而，轨道板下空洞缺陷的检测仍主要依靠铁路维修期间铁路工人的人工检查和探伤。如果不能迅速发现缺陷，后果可能是灾难性的。本文提出了一种非接触式动态检测轨道板下空洞缺陷的新方法。该方法是利用空气耦合超声传感器在轨道板中产生和接收超声导波，根据导波在传播过程中的能量泄漏原理，定量表示空隙缺陷的大小。以波束轴的位置为横坐标，时域信号的幅度为纵坐标，对位置-幅度曲线的特性进行了数值计算和分析。得到了位幅曲线凸间距与空隙缺陷大小的定量关系，提出了一种基于x、y二维线扫描数据融合的空隙缺陷成像方法。研究了空气耦合超声导波的激发和接收方法，发现1：实验室搭建了1个轨道结构模型，对方法进行验证，检测轨道板下的空隙缺陷。实验结果表明，空气耦合超声波传感器可以在轨道板中激发和接收超声波导波。基于导波漏能原理，可实现轨道板下空洞缺陷的定量表征和成像。